Method and apparatus for transmitting a signal by a radio frequency identification reader

ABSTRACT

A Radio Frequency Identification (RFID) reader is provided that receives a digital input signal, converts the digital input signal to an analog input signal, and determines whether the digital input signal is an unmodulated signal or is modulated with information. When the digital input signal is modulated with information, the RFID reader filters the analog input signal to produce a filtered analog input signal and transmits the filtered signal. When the digital input signal is an unmodulated signal, the RFID reader bypasses the filtering of the analog input signal to produce an unfiltered analog input signal and transmits the unfiltered analog input signal.

FIELD OF THE INVENTION

The present invention relates to Radio Frequency Identification (RFID)communication systems and, more particularly, to an RFID reader.

BACKGROUND OF THE INVENTION

Radio Frequency Identification (RFID) communications systems use passiveor active RFID tags that communicate with a fixed or handheld RFIDreader. In some instances, the reader provides an unmodulated carriersignal that is used to power a passive RFID tag. Communications from thepassive RFID tag back to the RFID reader then is accomplished byreflecting the unmodulated carrier signal at a predetermined rate,referred to as a backscatter signal. At other times, the RFID reader maytransmit information, modulated onto a carrier, to the RFID tag. When anRFID reader transitions between a state of transmitting an unmodulatedcarrier signal and a state of transmitting a modulated carrier signal,sideband noise of a modulated reader transmission can leak into areceiver circuitry of the RFID reader, thereby interfering with a lowlevel backscatter signal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIG. 1 is a block diagram of a Radio Frequency Identification (RFID)communication system in accordance with an embodiment of the presentinvention.

FIG. 2 is a block diagram of the RFID reader of FIG. 1 in accordancewith an embodiment of the present invention.

FIG. 3 is a block diagram of the RFID tag of FIG. 1 in accordance withan embodiment of the present invention.

FIG. 4 is a block diagram of a transmitter circuitry of the RFID readerof FIG. 1 in accordance with an embodiment of the present invention.

FIG. 5 is a logic flow diagram that illustrates an operation of the RFIDreader of FIG. 1 in accordance with an embodiment of the presentinvention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions and/or relative positioningof some of the elements in the figures may be exaggerated relative toother elements to help to improve understanding of various embodimentsof the present invention. Also, common but well-understood elements thatare useful or necessary in a commercially feasible embodiment are oftennot depicted in order to facilitate a less obstructed view of thesevarious embodiments of the present invention. It will further beappreciated that certain actions and/or steps may be described ordepicted in a particular order of occurrence while those skilled in theart will understand that such specificity with respect to sequence isnot actually required. Those skilled in the art will further recognizethat references to specific implementation embodiments such as“circuitry” may equally be accomplished via replacement with softwareinstruction executions either on general purpose computing apparatus(e.g., CPU) or specialized processing apparatus (e.g., DSP). It willalso be understood that the terms and expressions used herein have theordinary technical meaning as is accorded to such terms and expressionsby persons skilled in the technical field as set forth above exceptwhere different specific meanings have otherwise been set forth herein.

DETAILED DESCRIPTION OF THE INVENTION

An RFID reader is provided that receives a digital input signal,converts the digital input signal to an analog input signal, anddetermines whether the digital input signal is an unmodulated signal oris modulated with information. When the digital input signal ismodulated with information, the RFID reader filters the analog inputsignal to produce a filtered analog input signal and transmits thefiltered signal. When the digital input signal is an unmodulated signal,the RFID reader bypasses the filtering of the analog input signal toproduce an unfiltered analog input signal, and transmits the unfilteredanalog input signal, thereby filtering the signal to be transmitted whenfiltering is desired and bypassing the filtering when a mere continuouswave signal is being transmitted.

Generally, an embodiment of the present invention encompasses a methodfor transmitting a signal by an RFID reader. The method includesreceiving a digital input signal, converting the digital input signal toan analog input signal, determining whether the digital input signal isan unmodulated signal or is modulated with information, when the digitalinput signal is modulated with information, filtering the analog inputsignal to produce a filtered signal and transmitting the filteredsignal, and when the digital input signal is an unmodulated signal,bypassing the filtering of the analog input signal to produce anunfiltered analog input signal and transmitting the unfiltered analoginput signal.

Another embodiment of the present invention encompasses an RFID readercomprising a processor that is configured to produce a digital inputsignal and to determine whether the digital input signal is anunmodulated signal or is modulated with information. The RFID readerfurther comprises transmitter circuitry that is configured to transmit awireless signal, wherein the transmitter circuitry is configured toreceive the digital input signal, convert the digital input signal to ananalog input signal, when the digital input signal is modulated withinformation, filter the analog input signal to produce a filtered analoginput signal and transmit the filtered signal, and when the digitalinput signal is an unmodulated signal, bypass the filtering of theanalog input signal to produce an unfiltered analog input signal andtransmit the unfiltered analog input signal.

Yet another embodiment of the present invention encompasses anon-transitory computer-readable storage medium having computer readablecode stored thereon for programming a processor to perform the steps ofproviding a digital input signal to transmitter circuitry of a RadioFrequency Identification (RFID) reader, determining whether the digitalinput signal is an unmodulated signal or is modulated with information,when the digital input signal is modulated with information, control afiltering of an analog version of the digital input signal to produce afiltered analog input signal, and when the digital input signal is anunmodulated signal, control a bypassing of a filtering of the analogversion of the digital input signal to produce an unfiltered analoginput signal.

The present invention may be more fully described with reference toFIGS. 1-5. FIG. 1 is a block diagram of a Radio Frequency Identification(RFID) system 100 that includes an RFID reader 102 that generateswireless signals in order to read one or more RFID tags 104 (one shown)distributed about a monitored area. In accordance with variousembodiments of the present disclosure, RFID tag 104 may be an activetag, that is, a tag which has a self contained power supply or, as ismore usually the case, may be a passive tag that requires externalexcitation when it is to be read or interrogated within a monitored areaof RFID reader 102.

Referring now to FIGS. 2 and 3, block diagrams are provided thatillustrate RFID reader 102 and RFID tag 104 in accordance with anembodiment of the present invention. RFID reader 102 generates or emitsa radio-frequency (RF) interrogation signal (also sometimes called apolling signal). RFID tag 104 responds to the RF interrogation signal bygenerating an RF response signal that is transmitted back to RFID reader102 over an RF channel. The RF response signal is modulated in a mannerthat conveys identification data (that is, a tag identifier (ID)) forthe responding RFID tag back to the wireless tag reader. While reader102 is referred to herein as an RFID reader, one of ordinary skill inthe art realizes that reader 102 may be any type of wireless tag reader.For example, in large-scale applications, such as warehouses, retailspaces, and the like, many types of wireless tags may exist in theenvironment (or “site”) and, likewise, multiple types of wireless tagreaders, such as RFID readers, an active tag readers, 802.11 tagreaders, Zigbee tag readers, etc., may be used is such an environmentand may be linked together by a network controller or wireless switchesand the like.

Each of RFID reader 102 and RFID tag 104 includes a respective processor202, 302, such as one or more microprocessors, microcontrollers, digitalsignal processors (DSPs), combinations thereof or such other devicesknown to those having ordinary skill in the art. Each of RFID reader 102and RFID tag 104 further includes respective radio frequency (RF)transmitter circuitry 206, 306 and respective RF receiver circuitry 208,308 that are operationally coupled to their respective processors 202,302 and that provide for wirelessly transmitting and receiving signalsby the communication device.

Each of processors 202, 302 is operationally coupled to a respective atleast one memory device 204, 304, such as random access memory (RAM),dynamic random access memory (DRAM), and/or read only memory (ROM) orequivalents thereof, that maintains data and programs that may beexecuted by the processor and that allow the communication device toperform all functions necessary to operate in a wireless communicationsystem. For example, at least one memory device 204 of RFID reader 102includes instructions for assembling and transmitting an interrogationsignal via transmitter circuitry 206 of the RFID reader and forreceiving and processing of a backscatter signal received from RFID tag104 via receiver circuitry 208. Similarly, at least one memory device304 of RFID tag 104 includes instructions for receiving and processingof an interrogation signal received from RFID reader 104 via receivercircuitry 308 and for assembling and transmitting a backscatter signalto RFID reader 102 via transmitter circuitry 306 of the RFID tag.

As known in the art, when RFID tag 104 is a passive tag, the RFID reader102 provides an unmodulated carrier signal that is used to power theRFID tag. Communications from the RFID tag back to the RFID reader isaccomplished by reflecting the unmodulated RFID reader transmission at apredetermined rate, known as a backscatter signal. However, a problemarises in that this low level backscattered signal transmitted by theRFID tag may compete with sideband noise of a modulated carrier signalthat may be transmitted by RFID reader 102 and that leaks into receivercircuitry 208 of the RFID reader.

Referring now to FIG. 4, a block diagram is provided of transmittercircuitry 206 of RFID reader 102 in accordance with an embodiment of thepresent invention. Transmitter circuitry 206 includes an in-phase (I)signal path 401 and a quadrature-phase (Q) signal path 421. In-phasesignal path 401 includes a first digital-to-analog (D/A) converter 402coupled to a first switch 406. Switch 406 is, in turn, coupled to eachof a first filter 408, preferably an anti-aliasing filter, such as a lowpass filter or a band pass filter, and to a first filter bypass circuit410. Each of filter 408 and filter bypass circuit 410 then is coupled toa second switch 412 that is, in turn, coupled to a first modulator 416.Modulator 416 further is coupled to a signal combiner 444, and signalcombiner 444 is coupled to a radio frequency power amplifier (RFPA) 446.

Similarly, quadrature-phase (Q) signal path 421 includes a seconddigital-to-analog (D/A) converter 422 coupled to a third switch 426.Switch 426 is, in turn, coupled to each of a second filter 428,preferably an anti-aliasing filter, such as a low pass filter or a bandpass filter, and to a second filter bypass circuit 430. Each of filter428 and filter bypass circuit 430 then is coupled to a fourth switch 432that is, in turn, coupled to a second modulator 436. Modulator 436further is coupled to signal combiner 444, and, as noted above, signalcombiner 444 is coupled to RFPA 446.

Referring now to FIG. 5, a logic flow diagram 500 is provided thatillustrates an operation of RFID reader 102 in accordance with anembodiment of the present invention. More particularly, referring now toFIGS. 4 and 5, logic flow diagram 500 begins (502) when a digital inputsignal that is to be transmitted is provided (504) to transmittercircuitry 206 by processor 202 of RFID reader 102. The digital inputsignal may be an unmodulated signal, such as an interrogation signal, ormay be pre-modulated with information. Further, the digital input signalcomprises an in-phase (I) baseband component and a quadrature-phase (Q)baseband component, as known in the art.

Transmitter circuitry 206 routes the in-phase baseband component of thedigital input signal to in-phase signal path 401, which in turn routesthe in-phase baseband component to first D/A converter 402. Similarly,transmitter circuitry 206 routes the quadrature-phase baseband componentof the digital input signal to quadrature-phase signal path 421, whichin turn routes the quadrature-phase baseband component to second D/Aconverter 422. Transmitter circuitry 206 then converts (506) the digitalinput signal to an analog input signal. That is, D/A converter 402converts the in-phase baseband component to an analog in-phase signaland D/A converter 422 converts the quadrature-phase baseband componentto an analog quadrature-phase signal. D/A converter 402 then routes theanalog in-phase signal to switch 406, and D/A converter 422 routes theanalog quadrature-phase signal to switch 426.

An operation of each of switches 406, 412, 426, and 434 is controlled bya respective control signal 404/405, 414/415, 424/425, and 434/435received from processor 202. More particularly, processor 202 determines(508) whether the digital input signal is an unmodulated signal or ismodulated with information. When the digital input signal is anunmodulated signal, processor 202 operates switches 406, 412, 426, and434, to decouple filters 408 and 428 from a path of the analog signalsand to couple bypass circuits 410 and 430 to a path of the analogsignals, causing the analog signals to bypass (510) filters 408 and 428and thereby produce unfiltered analog signals. When the digital inputsignal is modulated with information, processor 202 operates switches406, 412, 426, and 434 to couple filters 408 and 428 to a path of theanalog signals and decouple bypass circuits 410 and 430 from a path ofthe analog signals, causing the analog signals to be routed (512) tofilters 408 and 428 and thereby produce filtered analog signals.

That is, if the digital input signal is an unmodulated signal, thenprocessor 202 controls transmitter circuitry 206 to switch filters 408and 428 out of the paths of the analog in-phase and quadrature-phasesignals and to switch bypass circuits 410 and 430 into the paths of theanalog in-phase and quadrature-phase signals. More particularly, if thedigital input signal is an unmodulated signal, processor 202 produces afirst multiple control signals 404, 414, 424, 434. Control signal 404causes switch 406 to couple D/A 402 to filter bypass circuit 410, andcontrol signal 414 causes switch 412 to couple filter bypass circuit 410to modulator 416. Thus, processor 202 causes the analog in-phase signalto bypass filter 408, thereby producing an unfiltered analog in-phasesignal, and routes the unfiltered analog in-phase signal to modulator416. Similarly, control signal 424 causes switch 426 to couple D/A 422to filter bypass circuit 430 and control signal 434 causes switch 432 tocouple filter bypass circuit 430 to modulator 436. Thus, processor 202causes the analog quadrature-phase signal to bypass filter 428, therebyproducing an unfiltered analog quadrature-phase signal, and routes theunfiltered analog quadrature-phase signal to modulator 436.

On the other hand, if the digital input signal is modulated withinformation, then processor 202 controls transmitter circuitry 206 toswitch filters 408 and 428 into the paths of the analog in-phase andquadrature-phase signals and to switch bypass circuits 410 and 430 outof the paths of the analog in-phase and quadrature-phase signals. Moreparticularly, if the digital input signal is modulated with information,processor 202 produces a second multiple control signals 405, 415, 425,and 435. Control signal 405 causes switch 406 to couple D/A 402 tofilter 408, and control signal 415 causes switch 412 to couple filter408 to modulator 416. Thus, the analog in-phase signal is routed tofilter 408, which produces a filtered analog in-phase signal, and filterbypass circuit 410 is skipped. Filter 408 then routes the filteredanalog in-phase signal to modulator 416. Similarly, control signal 425causes switch 426 to couple D/A 422 to filter 428, and control signal435 causes switch 432 to couple filter 428 to modulator 436. Thus, theanalog quadrature-phase signal is routed to filter 428, which produces afiltered analog quadrature-phase signal, and filter bypass circuit 430is skipped. Filter 428 then routes the filtered analog in-phase signalto modulator 436.

Transmitter circuitry 206 then upconverts (514) the analog signals to atransmission frequency based on a carrier signal, producing low powerradio frequency (RF) signals according to a signal modulation scheme.That is, modulator 416 receives a carrier signal from a local oscillator440 and upconverts the analog in-phase signal, received from eitherfilter bypass circuit 410 or filter 408, to a transmission frequencybased on the carrier signal, thereby producing a low power in-phaseradio frequency (RF) signal according to a signal modulation scheme. A90° phase shifter 442 is used to provide signals to modulate thein-phase and quadrature-phase components of the input signal. Similarly,modulator 436 receives a carrier signal from local oscillator 440 andupconverts the analog quadrature-phase signal, received from eitherfilter bypass circuit 430 or filter 428, to the transmission frequencybased on the carrier signal, producing a low power quadrature-phase RFsignal according to the signal modulation scheme. Again, 90° phaseshifter 442 is used to provide signals to modulate the in-phase andquadrature-phase components of the input signal.

Transmitter circuitry 206 then combines and amplifies (516) the lowpower RF signals signal to produce an RF output signal 448 fortransmission over the air, and transmits (518) the RF output signal.That is, transmitter circuitry 206 then routes, to signal combiner 444,each of the low power in-phase RF signal produced by modulator 416 andthe low power quadrature-phase RF signal produced by modulator 436.Signal combiner 444 combines the low power in-phase RF signal with thelow power quadrature-phase RF signal to produce a low power combinedsignal. Signal combiner 444 then routes the low power combined signal toRFPA 446, which provides power amplification of the low power combinedsignal to produce an RF output signal 448, which RF output signal istransmitted over the air by transmitter circuitry 206. Logic flowdiagram 500 then ends (520).

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

The benefits, advantages, solutions to problems, and any element(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeatures or elements of any or all the claims. The invention is definedsolely by the appended claims including any amendments made during thependency of this application and all equivalents of those claims asissued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has”,“having,” “includes”, “including,” “contains”, “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially”, “essentially”,“approximately”, “about” or any other version thereof, are defined asbeing close to as understood by one of ordinary skill in the art, and inone non-limiting embodiment the term is defined to be within 10%, inanother embodiment within 5%, in another embodiment within 1% and inanother embodiment within 0.5%. The term “coupled” as used herein isdefined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”) such asmicroprocessors, digital signal processors, customized processors andfield programmable gate arrays (FPGAs) and unique stored programinstructions (including both software and firmware) that control the oneor more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (e.g., comprising a processor) to perform amethod as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM (Read Only Memory), a PROM (Programmable Read OnlyMemory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM(Electrically Erasable Programmable Read Only Memory) and a Flashmemory. Further, it is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus, the following claimsare hereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

We claim:
 1. A method for transmitting a signal by a Radio FrequencyIdentification (RFID) reader, the method comprising: receiving a digitalinput signal; converting the digital input signal to an analog inputsignal; determining whether the digital input signal is an unmodulatedsignal or is modulated with information; when the digital input signalis modulated with information, filtering the analog input signal toproduce a filtered signal and transmitting the filtered signal; and whenthe digital input signal is an unmodulated signal, bypassing thefiltering of the analog input signal to produce an unfiltered analoginput signal and transmitting the unfiltered analog input signal.
 2. Themethod of claim 1, wherein filtering comprises filtering the analoginput signal with an anti-aliasing filter.
 3. The method of claim 2,wherein bypassing the filtering of the analog input signal comprisingswitching the anti-aliasing filter out of the path of the analog signal.4. The method of claim 1, wherein transmitting the filtered signalcomprises: upconverting the filtered signal to produce a low power radiofrequency (RF) signal; amplifying the low power RF signal to produce anoutput signal; and transmitting the output signal.
 5. The method ofclaim 1, wherein transmitting the unfiltered analog input signalcomprises: upconverting the unfiltered analog input signal to atransmission frequency to produce a low power radio frequency (RF)signal; amplifying the low power RF signal to produce an output signal;and transmitting the output signal.
 6. The method of claim 1, whereinthe digital input signal comprises an in-phase baseband component and aquadrature-phase baseband component; wherein converting the digitalinput signal to an analog input signal comprises converting the in-phasebaseband component to an analog in-phase signal and converting thequadrature-phase baseband component to an analog quadrature-phasesignal; wherein filtering the analog input signal to produce a filteredsignal and transmitting the filtered signal comprises: filtering theanalog in-phase signal to produce a filtered analog in-phase signal;filtering the analog quadrature-phase signal to produce a filteredanalog quadrature-phase signal; combining the filtered analog in-phasesignal and the filtered analog quadrature-phase signal to produce acombined signal; and transmitting the combined signal.
 7. The method ofclaim 6, wherein filtering the analog in-phase signal to produce afiltered analog in-phase signal comprises switching a first filter intoa path of the analog in-phase signal and wherein filtering the analogquadrature-phase signal to produce a filtered analog quadrature-phasesignal comprises switching a second filter into a path of the analogquadrature-phase signal.
 8. The method of claim 1, wherein the digitalinput signal comprises an in-phase baseband component and aquadrature-phase baseband component; wherein converting the digitalinput signal to an analog input signal comprises converting the in-phasebaseband component to an analog in-phase signal and converting thequadrature-phase baseband component to an analog quadrature-phasesignal; wherein bypassing the filtering of the analog input signal toproduce an unfiltered analog input signal and transmitting theunfiltered analog input signal comprises: bypassing a filtering of theanalog in-phase signal to produce an unfiltered analog in-phase signal;bypassing a filtering of the analog quadrature-phase signal to producean unfiltered analog quadrature-phase signal; combining the unfilteredanalog in-phase signal and the unfiltered analog quadrature-phase signalto produce a combined signal; and transmitting the combined signal. 9.The method of claim 8, wherein bypassing a filtering of the analogin-phase signal comprises switching a first bypass circuit into a pathof the analog in-phase signal, thereby bypassing a filtering of theanalog in-phase signal, and wherein bypassing a filtering of the analogquadrature-phase signal comprises switching a second bypass circuit intoa path of analog quadrature-phase signal, thereby bypassing a filteringof the analog quadrature-phase signal.
 10. A Radio FrequencyIdentification (RFID) reader comprising: a processor that is configuredto produce a digital input signal and to determine whether the digitalinput signal is an unmodulated signal or is modulated with information;transmitter circuitry that is configured to transmit a wireless signal,wherein the transmitter circuitry is configured to: receive the digitalinput signal; convert the digital input signal to an analog inputsignal; when the digital input signal is modulated with information,filter the analog input signal to produce a filtered analog input signaland transmit the filtered signal; and when the digital input signal isan unmodulated signal, bypass the filtering of the analog input signalto produce an unfiltered analog input signal and transmit the unfilteredanalog input signal.
 11. The RFID reader of claim 10, wherein theprocessor is configured to: when the digital input signal is anunmodulated signal, produce a first plurality of control signals thatcause the transmitter circuitry to bypass the filtering of the analoginput signal to produce an unfiltered analog input signal; and when thedigital input signal is modulated with information, produce a secondplurality of control signals that cause the transmitter circuitry tofilter the analog input signal to produce a filtered signal.
 12. TheRFID reader of claim 11, wherein the transmitter circuitry comprises:one or more bypass circuits; one or more filters; a plurality ofswitches coupled to each of the one or more bypass circuits and the oneor more filters; wherein, in response to receiving the first pluralityof control signals, the plurality of switches couple the one or morebypass circuits into a path of the analog input signal; and wherein, inresponse to receiving the second plurality of control signals, theplurality of switches couple the one or more filters into a path of theanalog input signal.
 13. The RFID reader of claim 12, wherein the one ormore filters are anti-aliasing filters.
 14. The RFID reader of claim 10,wherein the transmitter circuitry comprises: one or more modulators thatare configured to upconvert the filtered signal to produce a low powerradio frequency (RF) signal; a power amplifier that is configured toamplify the low power RF signal to produce an output signal; and whereinthe transmitter circuitry transmits the output signal.
 15. The RFIDreader of claim 10, wherein the transmitter circuitry comprises: one ormore modulators that are configured to upconvert the unfiltered analoginput signal to a transmission frequency produce a low power radiofrequency (RF) signal; a power amplifier that is configured to amplifythe low power RF signal to produce an output signal; and wherein thetransmitter circuitry is configured to transmit the output signal. 16.The RFID reader of claim 10, wherein the digital input signal comprisesan in-phase baseband component and a quadrature-phase baseband componentand wherein the transmitter circuitry comprises: a first digital toanalog converter (D/A) that is configured to convert the in-phasebaseband component to an analog in-phase signal; a second D/A that isconfigured to convert the quadrature-phase baseband component to ananalog quadrature-phase signal; a first filter that is configured tofilter the analog in-phase signal to produce a filtered analog in-phasesignal; a second filter that is configured to filter the analogquadrature-phase signal to produce a filtered analog quadrature-phasesignal; a signal combiner that is configured to combine the filteredanalog in-phase signal and the filtered analog quadrature-phase signalto produce a combined signal; and wherein the transmitter circuitry isconfigured to transmit the combined signal.
 17. The RFID reader of claim16, wherein the processor is configured to: control a switching of thefirst filter into a path of the analog in-phase signal; and control aswitching of the second filter into a path of the analogquadrature-phase signal.
 18. The RFID reader of claim 10, wherein thedigital input signal comprises an in-phase baseband component and aquadrature-phase baseband component and wherein the transmittercircuitry comprises: a first digital to analog converter (D/A) that isconfigured to convert the in-phase baseband component to an analogin-phase signal; a second D/A that is configured to convert thequadrature-phase baseband component to an analog quadrature-phasesignal; a first bypass circuit that is configured to bypass a filteringof the analog in-phase signal, thereby producing an unfiltered analogin-phase signal; a second bypass circuit that is configured to bypass afiltering of the analog quadrature-phase signal, thereby producing anunfiltered analog quadrature-phase signal; a signal combiner that isconfigured to combine the bypass analog in-phase signal and the bypassanalog quadrature-phase signal to produce a combined signal; and whereinthe transmitter circuitry is configured to transmit the combined signal.19. The RFID reader of claim 18, wherein the processor is configured to:control a switching of the first bypass circuit into a path of theanalog in-phase signal; and control a switching of the second bypasscircuit into a path of the analog quadrature-phase signal.
 20. Anon-transitory computer-readable storage medium having computer readablecode stored thereon for programming a processor to perform the steps of:providing a digital input signal to transmitter circuitry of a RadioFrequency Identification (RFID) reader; determining whether the digitalinput signal is an unmodulated signal or is modulated with information;when the digital input signal is modulated with information, control afiltering of an analog version of the digital input signal to produce afiltered analog input signal; and when the digital input signal is anunmodulated signal, control a bypassing of a filtering of the analogversion of the digital input signal to produce an unfiltered analoginput signal.
 21. The non-transitory computer-readable storage medium ofclaim 20, wherein controlling a filtering of the analog input signal toproduce a filtered signal comprises controlling a switch to couple afilter into the path of the analog version of the digital input signal,and wherein controlling a bypassing of a the filtering of the analoginput signal to produce an unfiltered analog input signal comprisescontrolling the switch to couple a bypass circuit into the path of ananalog version of the digital input signal, thereby bypassing thefilter.